Method of etching a surface of a substrate comprising LITAO{HD 3 {B and chemically similar materials

ABSTRACT

A method of etching a surface of a substrate comprising lithium tantalate (LiTaO3) and chemically similar materials is disclosed. The method includes contacting the surface with a mixture comprising hydrofluoric acid and sulfuric acid. In addition to its etching action, the mixture is also capable of polishing the thus treated surface.

United States Patent [191 Lim [451 Jan. 14,1975

[54] METHOD OF ETCHING A SURFACE OF A SUBSTRATE COMPRIS I N G LiTaO AND CHEMICALLY SIMILAR MATERIALS [75] Inventor: Mahn-Jick Lim, Lower Makefield Township, Bucks County, Pa.

[73] Assignee: Western Electric Company,

Incorporated, New York, NY.

22 Filed: Feb. 22, 1974 21 Appl. No.: 445,039

[52] US. Cl 156/17, 156/20, 252/793 [51] Int. Cl. H011 7/50 [58] Field of Search 156/2, 17, 20; 252/792,

K. Nassau et al., pp. 228 and 229, (Etching of UN- bO3).

Journal of Applied Physics, Domain Structure and Curie Temperature of Single-Crystal Lithium Tantalate by H. J. Levinstein et al., 6-22-1966, pp. 4585 and 4586.

Primary Examiner-Wil liam A. Powell Attorney, Agent, or FirmJ. Rosenstock [57] ABSTRACT A method of etching a surface of a substrate comprising lithium tantalate (LiTaO and chemically similar materials is disclosed. The method includes'contacting the surface with a mixture comprising hydrofluoric acid and sulfuric acid. In addition to its etching action, the mixture is also capable of polishing the thus treated surface.

4 Claims, No Drawings METHOD OF ETCHING A SURFACE OF A SUBSTRATE COMPRISING LiTaO AND CHEMICALLY SIMILAR MATERIALS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method of etching a surface of a substrate comprising LiTaO;, and chemically similar materials and more particularly, to a method of etching LiTaO with a mixture comprising hydrofluoric acid and sulfuric acid.

2. Description of the Prior Art Recently. lithium tantalate (LiTaO has become of great interest in the electrical device industry. An inherent problem in the use of LiTaO has been the etching and polishing of this material. Lithium tantalate (LiTaO can be etched with an aqueous mixture consisting of HNO and HF. However, the etching can only be carried out at a reasonable rate at the boiling temperature of the mixture. With respect to the polishing of LiTaO the HNO -HF mixture does not polish a surface of LiTAO so that optical inspection thereof for surface and interior defects is possible. An etchant ployed. In this regard, the temperature selected depends upon the parameters such as the etching mixture employed and the etch rate desired. After the substrate has been immersed in the etching solution mixture for.

- at 90C even after 40 hours of exposure thereto.

which both etches the LiTaO and polishes a surface thereof at a reasonable rate at a moderate temperature is therefore desirable and a method of employing such an etchant is an object of this invention.

SUMMARY OF THE INVENTION The present invention is directed to a method of etching a surface of a substrate comprising LiTaO and chemically similar materialsand more particularly, to

DETAILED DESCRIPTION The present invention is based upon the discovery of a-unique chemical system for etching lithium tantalate to be noted that a preferred mixture concentration for 49 weight percent aqueous HF and 97 weight percent aqueous H 50 typically ranges from about 0.40 to about 0.90 volume fraction of 49 weight percent aqueous HF (about 42.172 moles of HF/lOOO gms. H O, 40.173 moles of H SO,/1000 gms. H O to about 47.535 moles/1000 gms. H 0 and 3.354 moles/1000 gms. H O, respectively).

A substrate to be treated, i.e., comprising LiTaO is immersed in or exposed in some conventional manner to the-etching solution mixture wherein the LiTaO is etched. The temperature of the etching solution is maintained at a temperature between room temperature to the boiling point of the particular mixture em- Specific examples of the etching of a LiTaO substrate are as follows:

149 slices (AT cut) comprising LiTaO were ground to a 12p. finish. The samples were then immersed at C, in an etching solution comprising 65 volume percent of an aqueous 49 weight percent HF solution and 35 volume percent of an aqueous 97 weight percent H 80 solution. The samples were maintained in the etching solution for two hours to etch the surfaces thereof, i.e., to remove surface blemishes, damages and irregularities. After about two hours and a removal of 24 microns from the surfaces thereof, the samples were removed from the etchant solution and water rinsed.

Different samples from among the 149 etched slices were then subjected to varying volume fractions of aqueous 49 weight percent HF and aqueous 97 weight percent H 80 solutions at varying temperatures and time intervals. An etching rate for each sample. was then determined by measuring the weight change thereof and the area of each sample, using standard TABLE I (Temperature 25C) Molality of Molality of Volume HF (moles/ H,SO,(mules/ Etching Rate Fraction 100 g. H,O) 1000 g. H O) (um/hr.)

of HF TABLE 11 TABLE lV-Conlinued (Temperature 38C) (Tempcrutu re 64C) Vulume Fraction Etching Rule Volume Fraction Etching Rate 01' HF (um/hr) 5 of HF (um/hr.) 0 00 0 00671 090 0.00 0.00939 tag 6135?? 0.10 0.00671 0.10 0600402 0.20 04021117 0.20 0.03354 0.30 0.07915 TABLE V 0.31) 0.13684 0.35 0.20123 0.35 0.19318 (Tempelawre (Mu 01683] Volume Fraction Etchmg Rate 0.40 029514 (Mn/hm 0.45 0.30856 0.45 0.37027 012807 0.47 045345 010 004015 0.47 0.40783 0110 002281 0.50 0.46150 0-18782 0.60 0.59968 024551 (1.65 0.56346 030 151731 0.70 0.59029 20 35 44. 0.75 0.55004 31-08559 1 75 1513 2 0.40 3.33110 0.110 0.46955 0145 3-78052 0.110 0.34478 431580 0.90 0.23343 4-65790 1.00 0.18782 943950 1.00 0.13818 0.60 930,400 0.65 6.03703 0.65 6.17655 0.70 5.98336 0.70 6.28522 TABLE 0.75 5176871 0.75 4.77998 (Temperature 519C) Volume Fraction Etching Rate HF 1.00 1.74403 1.00 1.72122 0.00 005366 0.10 0.02683 0.20 0.03622 0.30 0.36893 0.30 0.43467 TABLE V! 0.35 040247 I 0140 0.80494 0.40 0.111030 1 (Temlmure 90C) J (L45 0'93 '04 Volume Fracuon Etchrng Rate 0.47 1.01556 0.61) 134156 40 060 1.51731 00965.9 0.65 1.32815 010 (160370 0.65 1.51596 010 035149 0.70 1.220112 030 174403 (m5 137778 0.30 1.80977 0.75 1.30131 295144 0.110 1.03300 313817 0.110 1.28253 339053 0.90 0.63053 5-57553 0.90 0.72713 0145 1.110 0.42930 1.00 0639710 797093 0.50 8.98846 50 0.50 8.65576 0.60 11.40327 0.60 9.45667 TABLE. IV 0.65 12.20821 0.65 10.82506 0.70 11.13496 (Temperature 64C) Q 10 05500 Volume Fraction Etching Rate 55 I 40327 01111 (um/hr.) 0.75 10.19453 v 0.80 10.46418 0.00 0.07379 0.90 7.51274 0.00 0.07513 0.90 7.34773 0.10 0.02415 1.00 4.42715 0.10 0.02146 1.00 5.08452 0.20 0.13416 0 1.00 4.25007 0.40 2.14650 0.45 2.16796 0.47 2.54897 1147 21,2275 Spec1f1c examples of pohshlng a L1Ta0 substrate are 0.47- 2.19479 0.50 2.03917 as u M0 295144 1. A l1th1um tantalate (L1TaO sllce (AT cut) was 1 3 3 ground to a 12p. finlsh. The slice was then immersed at Z2 C for 30 mmutes, 1n an aqueous mrxture comprlsmg 65 volume percent HF (49 weight percent) and 35 volume percent H SO (97 weight percent). The thus treated slice was rendered semi-opaque thereby enabling optical examination by conventional apparatus and means for gross defects therein.

2. The procedure of (1) above was repeated except that the slice was immersed in the mixture for four hours. The slice was rendered almost transparent as il he!i.n t 9r ehc tp lis c What is claimed is: v

l. A. method of etching a surface of a substrate comprising LiTaO which comprises contacting the surface with a mixture comprising HF present in an amount ranging from about 42.172 to about 47.535 molal and H 80 present in an amount ranging from about 40.173 to about 3.354 molal.

2. A method of treating a body comprising lithium 4. The method as defined in claim 3 which further comprises directly examining said treated substrate with optical means.

L SSS-PT UNITED STATES PATENT CFFICE CERTIFICATE OF CQRRECTION PatenrNo. 3 ate January 1 1975 lnventor(s) Mahn-Jick Lim It is certified that error appears in the above-identified parent and that said Letters Patent are hereby corrected as shown below:

In the specification, Column 2, Table I, Second Column Heading, "100 g." should read --lOOO g.; second column, "43,23 should read 'r5.23 L-; fourth column, "1.22672 should read --o.22672--. Column 3,

Table)III, Second Column Heading, "hr. should read Signed and sealed this 11th day of March 1975 (SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks 

2. A method of treating a body comprising lithium tantalate to obtain a polished surface thereof, which comprises contacting the surface with a mixture comprising HF present in an amount ranging from about 42.172 to about 47.535 molal and H2SO4 present in an amount ranging from about 40.173 to about 3.354 molal.
 3. A method of optically examining a substrate comprising LiTaO3 which comprises treating the substrate with a mixture comprising HF present in an amount ranging from about 42.172 molal to about 47.535 molal and H2SO4 present in an amount ranging from about 40.173 to about 3.354 molal.
 4. The method as defined in claim 3 which further comprises directly examining said treated substrate with optical means. 